1. Field of the Invention
The present invention relates to a plating substrate composed of a copper plating film provided on a glass base material or a ceramic base material, having at least an oxide on a surface thereof, an electroless plating method forming a copper plating film, and a circuit forming method using the aforementioned method.
2. Description of the Related Art
Heretofore, for example, as a method for forming a plating film on a glass base material or a ceramic base material, an electroless copper plating method has been known (for example, see Japanese Unexamined Patent Application Publication Nos. 2000-54153, 2003-13247, and 2004-332023).
In a related electroless copper plating method, in order to ensure high adhesion between a surface of a base material and a copper plating film formed thereon by an anchor effect, first, the surface is intensively processed by surface roughening treatment, so that coarse irregularities are formed on the surface.
Subsequently, a ceramic base material processed by the roughening treatment is immersed in a copper plating solution, so that a copper plating film is formed on the ceramic base material.
However, when the copper plating film, which is provided on the surface of the ceramic base material processed by the roughening treatment, is used as an electrode of a dielectric resonator or the like, an electrode having a wiring pattern with a pitch of approximately 100 μm may be formed; however, it becomes difficult to form an electrode having a wiring patter with a pitch of approximately 20 μm, and as a result, there has been a limit to form an electrode having a fine pitch wiring pattern.
In addition, in the dielectric resonator as described above, the Q is decreased in a non-load state, and as a result, high frequency properties are disadvantageously degraded.
Furthermore, the problem described above becomes more serious when coarser irregularities are formed on the surface by surface roughening treatment. Accordingly, as disclosed in Japanese Unexamined Patent Application Publication No. 2000-54153, for example, an electroless copper plating method has been proposed in which even when the irregularities are formed on the surface as fine as possible by roughening treatment, excellent adhesion of a copper plating film to the surface thus processed is ensured.
In the electroless copper plating method as described above, after fine irregularities are formed on the surface of a ceramic base material by roughening treatment, a copper plating film is formed by immersing the ceramic base material processed by the roughening treatment in a copper plating solution. In this case, according to the electroless copper plating method disclosed in Japanese Unexamined Patent Application Publication No. 2000-54153, in order to increase the adhesion of the copper plating film to the surface on which the fine irregularities are formed, 0.01 to 1.0 mole of nickel ions is contained in a copper plating solution with relative to 100 moles of copper contained therein. As described above, even when the irregularities formed on the surface are fine, the copper plating solution is prepared so as to ensure high adhesion of the copper plating film to the surface thus processed.
As described above, according to Japanese Unexamined Patent Application Publication No. 2000-54153, even when the irregularities formed on the surface are fine, the copper plating film can be favorably adhered to the surface; however, even by the electroless copper plating method described above, it is required that the roughening treatment be performed on the surface of the ceramic base on which the plating is to be performed. However, in order to form a fine pitch wiring pattern and to further improve the high frequency properties, it has been desired that the surface of the base material be mirror finished.
In addition, since hydrogen fluoride is used in one step of the roughening treatment, waste disposal treatment is also required, the number of production steps is increased, and as a result, the production cost is disadvantageously increased. Hence, in view of environmental conservation and reduction in production cost, it is preferable that the roughening treatment be not performed.
However, when a copper plating film is formed on a mirror-finished surface of the ceramic base material, a problem may arise in that the adhesion of the copper plating film to the surface is considerably decreased.